1. Field of Invention
The present invention relates to a cooling system, a vehicle equipped with the cooling system, and a method for controlling the cooling system.
2. Description of Related Art
A system that is mounted on a vehicle and that uses a fan for cooling a battery has been described in which, if the temperature of the battery is equal to or below a specified maximum threshold temperature, the fan is driven while the control duty ratio that is required based on the temperature and the heat generation amount of the battery is limited to maintain an acceptable noise level of the operating noise of the fan in accordance with the vehicle speed (for example, see Japanese Patent Application Publication No. 2003-178815 (JP-A-2003-178815)). In another example of a battery cooling system of this type, the fan is driven using a duty ratio that is determined in view of noise based on the vehicle speed and the engine speed as well as the temperature of the battery (for example, see Japanese Patent Application Publication No. 2005-184979 (JP-A-2005-184979)).
In the cooling systems described above, reliable activation of the fan is necessary when a target object such as a battery should be cooled. However, if the duty ratio used to activate the fan is set high to allow reliable activation of the fan, the rotational speed of the fan may be excessive, resulting in excessive operating noise.